In the oilfield industry, it is becoming more common to employ continuous coiled rod instead of conventional sucker rod, for example for the purpose of driving downhole pump equipment, thereby avoiding the need to thread together discrete rod sections via threaded couplers at the ends thereof, and instead using an injector to feed a continuous rod string into the well from a coiled supply of the continuous rod. Such injectors typically employ a pair of endless chains driven in counter-rotating directions in a common upright plane, and carrying gripper dies or blocks on the chains that have outward facing gripping surfaces to clench the continuous rod between the faces of opposed gripper dies on the two chains as they descend downward on adjacent, facing-together, parallel sides of the two chain paths. A respective skate is found inside the area around which each train is driven to lie along this descending side of the chain, and is displaceable against this side of the chain by hydraulic cylinders, thereby forcing the descending gripper blocks together to firmly grip the continuous rod between them.
U.S. Pat. Nos. 6,880,629 and 8,132,617 disclose grippers for continuous coiled rod injector heads, and each prescribe the use of aluminum at the rod-engaging face of the gripper to avoid scarring or damage the continuous rod that was found or expected to occur if hardened steel was instead used, as was previously proposed for use in coiled tubing applications.
However, Applicant has found that use of aluminum grippers for continuous rod injection has its shortcomings, particularly in that high skate pressures are required to attain sufficient grip, and that injector components undergo notable wear in such high pressure conditions, limiting the effective lifespan of these components.
Accordingly, there remains room for improvement in the area of gripper dies for specific use with continuous coiled rod.
Other prior art in the general area of injector heads and gripper dies for same include U.S. Pat. Nos. 5,094,340, 6,425,441, 6,609,566, 6,892,810, 7,857,042 and U.S. Patent Application Publication 2012/0222855, but these are directed primarily toward coiled tubing applications, and don't address the need for improved solutions in the particular area of continuous coiled rod.